This invention relates to pipeline leakage detection and more particularly to a wireless communication system for transmitting leakage information to a remote location.
Water leakage can reach 30% on average of the water transported across the water distribution networks [1, 2]. Many different techniques have been developed to detect leaks, either from the inside [3, 4] or from the outside of pipes [5]. Studies [3] have shown that compared with outside-of-the-pipe inspection, in-pipe inspection is much more accurate. In-pipe inspections are less sensitive to random events and external noise as well as less subjective to the operator's experience.
Communication functions are extremely important for an in-pipe inspection system to provide effective leak detection. For accurate and real-time leak detection, the sensed information needs to be reliably and timely transmitted to a remote monitoring center. On the other hand, in-pipe sensor nodes may need to be remotely controlled by the remote monitoring center, and accurate and timely delivery of control commands from the remote monitoring center to the in-pipe sensor nodes also poses a high requirement on the communication system.
There are several critical challenges on the development of a communication system for in-pipe inspection. First, traditional wired communication systems [6] do not work well. Wired systems have several drawbacks, such as limited scanning range, limited sensor mobility, and system failure due to wire damage. Second, for wireless communication systems, signals need to travel through different media, including water, plastic, soil, and air, to reach aboveground. Third, the battery-based energy supply of the in-pipe sensor nodes is limited. Finally, the motion of the in-pipe sensor nodes results in dynamic communication links and network connectivity.
In recent years some systems have been developed to provide wireless data communications for pipeline impaction or underground infrastructure monitoring. Different technologies have been explored to enable wireless communication, such as radio communications, acoustic communications, magnetic induction, elastodynamic waves, etc.
Some works adopt radio communications to enable information transmission for in-pipe inspection. Published application number 2005/0145018 describes a method for remote monitoring of a gas pipeline using wireless sensor networks. Wireless motes and nodes are deployed to some identified locations in the pipeline by a robot. Data from sensors are transmitted to some access points by using radio communications. Wireless transmitters operate inside the pipe such that the metal pipe acts as waveguide for the electromagnetic radiation. However this wireless communication method may not work well with water pipelines due to the high attenuation of radio waves in water. Also, the work is not focused on underground scenarios. U.S. Pat. No. 7,607,351 discloses a pipeline monitoring system with sensors placed along the pipeline. Each sensor station is equipped with a satellite modem and satellite antenna to provide near real time bidirectional communications between the sensor station and the remote monitoring center. However, sensors are affixed to the outside of the pipeline, making it difficult to detect small leaks or damage to the pipeline. There have been some research works on in-pipe inspection systems using radio communications [4]. However sensors in those systems are deployed at some fixed check points inside the pipe, which is unfeasible for performing sensing very close to a leak.
Some works developed wireless communication systems in the pipelines using acoustic waves. U.S. Pat. No. 7,423,931 discloses an acoustic system for communications in pipelines. A transmitter located in the pipeline communicates with a receiver by emitting acoustic signal bursts using the pipeline as a wave-guide or channel. To provide high data rate transmission, a frequency range of 3-100 kHz is adopted. However, the designers make no explanation of how to transmit the information from an underground pipeline to aboveground devices. The authors in [9] also use an acoustic wave to transmit sensing data in the pipe. However, two of the major challenges associated with acoustic communication systems are limited transmission bandwidth and high power consumption. These drawbacks make acoustic communication systems unsuitable for monitoring long pipelines with different pipe geometries.
Some works focus on magnetic induction based wireless communication systems for underground or underwater applications. U.S. Pat. No. 7,831,205 discloses a network of magnetic induction units that is configured to transmit a signal to or receive a signal from neighboring units by modulation of a time-varying magnetic field. Underground or underwater monitoring applications are suggested with the sensed data relayed in a multi-hop fashion. Some researchers have also proposed magnetic induction (MI)-based communications to wirelessly transmit data with the use of coils of wire wound on the pipelines [10]. However, in view of the short range of communications between two neighboring magnetic induction units or coils, it is impossible to perform large-scale deployment of such units or coils on long underground pipelines.
Some works adopt elastodynamic waves to enable wireless communications. U.S. Pat. No. 7,602,668 describes down hole sensor networks using wireless communications. The communication link between a sensor and a hub in the wellbore is formed by using elastodynamic waves. However, this wireless communication method is unsuitable for in-pipe inspection systems due to deployment challenges.
Thus, there is a need for a wireless communication system for underground in-pipe monitoring with mobile sensor nodes. Once such a system is in place, then pipelines can be monitored with a long-range and long-time operation in an accurate and real-time way.